Name{number} snapraid - SnapRAID Backup For Disk Arrays Synopsis :snapraid [-c, --conf CONFIG] : [-f, --filter PATTERN] [-d, --filter-disk NAME] [-m, --filter-missing] : [-a, --audit-only] [-i, --import DIR] : [-N, --find-by-name] : [-Z, --force-zero] [-E, --force-empty] [-U, --force-uuid] : [-s, --start BLKSTART] [-t, --count BLKCOUNT] : [-v, --verbose] [-l, --log FILE] : sync|pool|diff|dup|check|fix :snapraid [-V, --version] [-h, --help] Description SnapRAID is a backup program for a disk array. SnapRAID stores redundancy information in the disk array, and it allows recovering from up to two disk failures. SnapRAID is mainly targeted for a home media center, where you have a lot of big files that rarely change. Beside the ability to recover from disk failures, the other features of SnapRAID are: * You can start using SnapRAID with already filled disks. * The disks can have different sizes. * You can add disks at any time. * If you accidentally delete some files in a disk, you can recover them. * If more than two disks fail, you lose the data only on the failed disks. All the data in the other disks is safe. * It doesn't lock-in your data. You can stop using SnapRAID at any time without the need to reformat or move data. * All your data is hashed to ensure data integrity and to avoid silent corruption. The official site of SnapRAID is: :http://snapraid.sourceforge.net Limitations SnapRAID is in between a RAID and a Backup program trying to get the best benefits of them. Although it also has some limitations that you should consider before using it. The main one is that if a disk fails, and you haven't recently synced, you may not able to do a complete recover. More specifically, you may be unable to recover up to the size of the amount of the changed or deleted files from the last sync operation. This happens even if the files changed or deleted are not in the failed disk. New added files don't prevent the recovering of the already existing files. You may only lose the just added files, if they are on the failed disk. This is the reason because SnapRAID is better suited for data that rarely change. Other limitations are: * You have different file-systems for each disk. Using a RAID you have only a big file-system. * It doesn't stripe data. With RAID you get a speed boost with striping. * It doesn't support real-time recovery. With RAID you do not have to stop working when a disk fails. * It's able to recover damages only from up to two disks. With a Backup you are able to recover from a complete failure of the whole disk array. * Only file, timestamps, symlinks and hardlinks are saved. Permissions, ownership and extended attributes are not saved. Getting Started To use SnapRAID you need to first select one disk of your disk array to dedicate at the "parity" information. With one disk for parity you will be able to recover from a single disk failure, like RAID5. If you want to recover from two disk failures, like RAID6, you must reserve another disk for the "q-parity" information. As parity disks, you have to pick the biggest disks in the array, as the redundancy information may grow in size as the biggest data disk in the array. These disks will be dedicated to store the "parity" and "q-parity" files. You should not store your data in them. The list of files is saved in the "content" files, usually stored in the data, parity or boot disks. These files contain the details of your backup, with all the checksums to verify its integrity. The "content" file is stored in multiple copies, and each one must be in a different disk, to ensure that in even in case of multiple disk failures at least one copy is available. For example, suppose that you are interested only at one parity level of protection, and that your disks are present in: :/mnt/diskpar <- selected disk for parity :/mnt/disk1 <- first disk to backup :/mnt/disk2 <- second disk to backup :/mnt/disk3 <- third disk to backup you have to create the configuration file /etc/snapraid.conf with the following options: :parity /mnt/diskpar/parity :content /var/snapraid/content :content /mnt/disk1/content :content /mnt/disk2/content :disk d1 /mnt/disk1/ :disk d2 /mnt/disk2/ :disk d3 /mnt/disk3/ If you are in Windows, you should use drive letters and backslashes instead of slashes, and if you like, also file extensions. :parity E:\par\parity.par :content C:\snapraid\content.lst :content F:\array\content.lst :content G:\array\content.lst :disk d1 F:\array\ :disk d2 G:\array\ :disk d3 H:\array\ At this point you are ready to start the "sync" command to build the redundancy information. :snapraid sync This process may take some hours the first time, depending on the size of the data already present in the disks. If the disks are empty the process is immediate. You can stop it at any time pressing Ctrl+C, and at the next run it will start where interrupted. When this command completes, your data is SAFE. At this point you can start using your array as you like, and periodically update the redundancy information running the "sync" command. Pooling To have all the files in your array shown in the same directory tree, you can enable "pooling", that consists in creating a virtual view of all the files in your array using symbolic links. You can configure the "pooling" directory in the configuration file with: :pool /pool or, if you are in Windows, with: :pool C:\pool and then run the "pool" command. :snapraid pool Checking & Fixing To check the integrity of your data you can use the "check" command: :snapraid check If will read all your data, to check if it's correct. If an error is found, you can use the "fix" command to fix it. :snapraid fix Note that the fix command will revert your data at the state of the last "sync" command executed. It works like a snapshot was taken in "sync". In this regard SnapRAID is more like a backup program than a RAID system. For example, you can use it to recover from an accidentally deleted directory, simply running the fix command using the -m, --filter-missing filter, like: :snapraid fix -m -f DIR/ Or to simply recover one file you can use: :snapraid fix -m -f FILE Or to recover all the delete files with: :snapraid fix -m Commands SnapRAID provides four simple commands that allow to: * Make a backup/snapshot -> "sync" * See the files changed from the previous sync -> "diff" * Check for integrity -> "check" * Restore the last backup/snapshot -> "fix". Take care that the commands have to be written in lower case. sync Updates the redundancy information. All the modified files in the disk array are read, and the redundancy data is recomputed. Files are identified by inode and checked by time and size, meaning that you can move them on the disk without triggering any redundancy recomputation. You can stop this process at any time pressing Ctrl+C, without losing the work already done. The "content", "parity" and "q-parity" files are modified if necessary. The files in the array are NOT modified. pool Creates or updates in the "pooling" directory a virtual view of all the files of your disk array. The files are not really copied here, but just linked using symbolic links. When updating, all the present symbolic links and empty subdirectories are deleted and replaced with the new view of the array. Any othe regular file is left in place. Nothing is modified outside the pool directory. diff Lists all the files modified from the last "sync" command that have to recompute their redundancy data. Nothing is modified. dup Lists all the duplicate files. Two files are assumed equal if their hashes are matching. The effective data is not read. Nothing is modified. check Checks all the files and the redundancy data. All the files are hashed and compared with the snapshot saved in the previous "sync" command. If you use the -a, --audit-only option, only the file data is checked, and the redundandy data is ignored. Files are identified by path, and checked by content. Nothing is modified. fix Checks and fix all the files. It's like "check" but it also tries to fix problems reverting the state of the disk array to the previous "sync" command. After a successful "fix", you should also run a "sync" command to update the new state of the files. All the files that cannot be fixed are renamed adding the ".unrecoverable" extension. The "content" file is NOT modified. The "parity" and "q-parity" files are modified if necessary. The files in the array are modified if necessary. Options SnapRAID provides the following options: -c, --conf CONFIG Selects the configuration file. If not specified it's assumed the file "/etc/snapraid.conf" in Unix, and "snapraid.conf" in the current directory in Windows. -f, --filter PATTERN Filters the files to process in the "check" and "fix" commands. Only the files matching the entered pattern are processed. This option can be used many times. See the PATTERN section for more details in the pattern specifications. In Unix, ensure to quote globbing chars if used. This option can be used only with the "check" and "fix" commands. Note that it cannot be used with "sync", because "sync" always process the whole array. -d, --filter-disk NAME Filters the files to process in the "check" and "fix" commands. Only the files present in the specified disk are processed. You must specify a disk name as named in the configuration file. In "check", you can make it faster, specifing also -a, --audit-only option, to avoid to access other disks to check parity data. If you combine more --filter, --filter-disk and --filter-missing options, only files matching all the set of filters are selected. This option can be used many times. This option can be used only with the "check" and "fix" commands. Note that it cannot be used with "sync", because "sync" always process the whole array. -m, --filter-missing Filters the files to process in the "check" and "fix" commands. Only the files missing/deleted from the array are processed. When used with "fix", this is a kind of "undelete" command. If you combine more --filter, --filter-disk and --filter-missing options, only files matching all the set of filters are selected. This option can be used only with the "check" and "fix" commands. Note that it cannot be used with "sync", because "sync" always process the whole array. -a, --audit-only When checking, only verify the hash of the files, without doing any kind of check on the redundancy data. If you are interested in checking only the file data this option can speedup a lot the checking process. This option can be used only with the "check" command. -i, --import DIR When fixing imports from the specified directory any file that you deleted from the array after the last "sync" commmand. If you still have such files, they could be used by the "fix" command to improve the recover process. The files are read also in subdirectories and they are identified regardless of their name. This option can be used only with the "check" and "fix" command. -N, --find-by-name When syncing finds the files by path instead than by inode, and ignores the nanosecond part of timestamp. This option allows a fast sync command after having replaced one physical disk with another, copying manually the files. Without this option the "sync" command recognizes that the files were copied to a different disk, and it will resync them all. With this option, a file with the correct path, size and time with second precision is assumed identical at the previous one, and not resynched. The nanosecond part of timestamps is ignored because most of copy programs are not able to correctly restore it. This option can be used only with the "sync" and "diff" commands. -Z, --force-zero Forces the insecure operation of syncing a file with zero size that before was not. If SnapRAID detects a such condition, it stops proceeding unless you specify this option. This allows to easily detect when after a system crash, some accessed files were zeroed. This is a possible condition in Linux with the ext3/ext4 filesystems. This option can be used only with the "sync" command. -E, --force-empty Forces the insecure operation of syncing a disk with all the original files missing. If SnapRAID detects that all the files originally present in the disk are missing or rewritten, it stops proceeding unless you specify this option. This allows to easily detect when a data file-system is not mounted. This option can be used only with the "sync" command. -U, --force-uuid Forces the insecure operation of syncing, checking and fixing with disks that have changed the UUID. If SnapRAID detects that some disks have changed UUID, it stops proceeding unless you specify this option. This allows to detect when your disks are mounted in the wrong mount points. It's anyway allowed to have a single UUID change with single parity, and two with double parity, because it's the normal case of replacing disks. This option can be used only with the "sync", "check" or "fix" command. -s, --start BLKSTART Starts the processing from the specified block number. It could be useful to easy retry to check or fix some specific block, in case of a damaged disk. -t, --count BLKCOUNT Process only the specified number of blocks. It's present mainly for advanced manual recovering. -l, --log FILE Outputs a detailed log to the specified file. It contains the exact specification of which block of any file is not recoverable and why. If this option is not specified, the log is printed in the console using the standard error stream. -v, --verbose Prints more information in the processing. -h, --help Prints a short help screen. -V, --version Prints the program version. Configuration SnapRAID requires a configuration file to know where your disk array is located, and where storing the redundancy information. This configuration file is located in /etc/snapraid.conf in Unix or in the execution directory in Windows. It should contain the following options (case sensitive): parity FILE Defines the file to use to store the parity information. The parity enables the protection from a single disk failure, like RAID5. It must be placed in a disk dedicated for this purpose with as much free space as the biggest disk in the array. Leaving the parity disk reserved for only this file ensures that it doesn't get fragmented, improving the performance. This option is mandatory and it can be used only one time. q-parity FILE Defines the file to use to store the q-parity information. If present, the q-parity enables the protection from two disk failures, like RAID6. It must be placed in a disk dedicated for this purpose with as much free space as the biggest disk in the array. Leaving the q-parity disk reserved for only this file ensures that it doesn't get fragmented, improving the performance. This option is optional and it can be used only one time. content FILE Defines the file to use to store the list and checksums of all the files present in your disk array. It can be placed in the disk used to store data, parity, or any other disk available. If you use a data disk, this file is automatically excluded from the "sync" process. This option is mandatory and it can be used more time to save more copies of the same files. You have to store at least one copy for each parity disk used plus one. Using some more don't hurt. disk NAME DIR Defines the name and the mount point of the disks of the array. NAME is used to identify the disk, and it must be unique. DIR is the mount point of the disk in the filesystem. You can change the mount point as you like, as long you keep the NAME fixed. You should use one option for each disk of the array. nohidden Excludes all the hidden files and directory. In Unix hidden files are the ones starting with ".". In Windows they are the ones with the hidden attribute. exclude/include PATTERN Defines the file or directory patterns to exclude and include in the sync process. All the patterns are processed in the specified order. If the first pattern that matches is an "exclude" one, the file is excluded. If it's an "include" one, the file is included. If no pattern matches, the file is excluded if the last pattern specified is an "include", or included if the last pattern specified is an "exclude". See the PATTERN section for more details in the pattern specifications. This option can be used many times. block_size SIZE_IN_KIBIBYTES Defines the basic block size in kibi bytes of the redundancy blocks. Where one kibi bytes is 1024 bytes. The default is 256 and it should work for most conditions. You could increase this value if you do not have enough RAM memory to run SnapRAID. As a rule of thumb, with 4 GiB or more memory use the default 256, with 2 GiB use 512, and with 1 GiB use 1024. In more details SnapRAID requires about TS*24/BS bytes of RAM memory to run. Where TS is the total size in bytes of your disk array, and BS is the block size in bytes. For example with 6 disk of 2 TiB and a block size of 256 KiB (1 KiB = 1024 Bytes) you have: :RAM = (6 * 2 * 2^40) * 24 / (256 * 2^10) = 1.1 GiB You could instead decrease this value if you have a lot of small files in the disk array. For each file, even if of few bytes, a whole block is always allocated, so you may have a lot of unused space. As approximation, you can assume that half of the block size is wasted for each file. For example, with 10000 files and a 256 KiB block size, you are going to waste 1.2 GiB. autosave SIZE_IN_GIBIBYTES Automatically save the state when synching after the specied amount of GiB processed. This option is useful to avoid to restart from scratch long "sync" commands interrupted by a machine crash, or any other event that may interrupt SnapRAID. The SIZE argument is specified in gibibytes. Where one gibi bytes is 1073741824 bytes. pool DIR Defines the pooling directory where the virtual view of the disk array is created using the "pool" command. The directory must already exist. Examples An example of a typical configuration for Unix is: :parity /mnt/diskpar/parity :content /mnt/diskpar/content :content /var/snapraid/content :disk d1 /mnt/disk1/ :disk d2 /mnt/disk2/ :disk d3 /mnt/disk3/ :exclude *.bak :exclude /lost+found/ :exclude /tmp/ An example of a typical configuration for Windows is: :parity E:\par\parity :content E:\par\content :content C:\snapraid\content :disk d1 G:\array\ :disk d2 H:\array\ :disk d3 I:\array\ :exclude *.bak :exclude Thumbs.db :exclude \$RECYCLE.BIN :exclude \System Volume Information Pattern Patterns are used to select a subset of files to exclude or include in the process. There are four different types of patterns: =FILE Selects any file named as FILE. You can use any globbing character like * and ?. This pattern is applied only to files and not to directories. =DIR/ Selects any directory named DIR. You can use any globbing character like * and ?. This pattern is applied only to directories and not to files. =/PATH/FILE Selects the exact specified file path. You can use any globbing character like * and ? but they never match a directory slash. This pattern is applied only to files and not to directories. =/PATH/DIR/ Selects the exact specified directory path. You can use any globbing character like * and ? but they never match a directory slash. This pattern is applied only to directories and not to files. In Windows you can freely use the backslash \ instead of the forward slash /. Note that Windows system directories, junction to directories, mount points, and any other Windows special directory is treated just as a file, meaning that to exclude it you must use a file rule, and not a directory one. In the configuration file, you can use different strategies to filter the files to process. The simplest one is to use only "exclude" rules to remove all the files and directories you do not want to process. For example: :# Excludes any file named "*.bak" :exclude *.bak :# Excludes the root directory "/lost+found" :exclude /lost+found/ :# Excludes any sub-directory named "tmp" :exclude tmp/ The opposite way is to define only the file you want to process, using only "include" rules. For example: :# Includes only some directories :include /movies/ :include /musics/ :include /pictures/ The final way, is to mix "exclude" and "include" rules. In this case take care that the order of rules is important. Previous rules have the precedence over the later ones. To get things simpler you can first have all the "exclude" rules and then all the "include" ones. For example: :# Excludes any file named "*.bak" :exclude *.bak :# Excludes any sub-directory named "tmp" :exclude tmp/ :# Includes only some directories :include /movies/ :include /musics/ :include /pictures/ On the command line, using the -f option, you can only use "include" patterns. For example: :# Checks only the .mp3 files. :# Note the "" use to avoid globbing expansion by the shell in Unix. :snapraid -f "*.mp3" check In Unix, when using globbing chars in the command line, you have to quote them. Otherwise the shell will try to expand them. Recovering The worst happened, and you lost a disk! DO NOT PANIC! You will be able to recover it! The first thing you have to do is to avoid futher changes at you disk array. Disable any remote connection to it, any scheduled process, including any scheduled SnapRAID nightly sync. Then proceed with the following steps. STEP 1 -> Reconfigure You need some space to recover, even better if you already have an additional disk, but in case, also an external USB or remote one is enough. Change the SnapRAID configuration file and make the "disk" option of the failed disk to point to a place where you have enough empty space to recover the files. For example, if you have that disk "d1" failed, you can change: :disk d1 /mnt/disk1/ to: :disk d1 /mnt/new_spare_disk/ STEP 2 -> Fix Run the fix command, storing the log in an external file with: :snapraid -d NAME -l fix.log fix Where NAME is the name of the disk, like "d1" as in our previous example. This command will take a long time. You can also add the '-v' option to see on the console the fixed files. Take care that you need also few gigabytes free to store the fix.log file. Run it from a disk with some free space. Now you have recovered all the recoverable. If some file is partially or totally unrecoverable, it will be renamed adding the ".unrecoverable" extension. You can get a detailed list of all the unrecoverable blocks in the fix.log file checking all the lines starting with "unrecoverable:" If you are not satified of the recovering, you can retry it as many time you wish. For example, if you have moved away some files from other disks after the last "sync", you can retry to put them inplace, and retry the "fix". If you are satisfied of the recovering, you can now proceed further, but take care that after synching you will no more able to retry the "fix" command! STEP 3 -> Check As paranoid but recommended check, you can now run a "check" command to ensure that everything is OK on the disk. :snapraid -d NAME -a check Where NAME is the name of the disk, like "d1" as in our previous example. The options -d and -a tell SnapRAID to check only the specified disk, and ignore all the other data and redundancy disks. This command will take a long time. STEP 4 -> Sync Run the "sync" command to resyncronize the array with the new disk. To avoid a long time sync you can use the "--find-by-name" option to force SnapRAID to ignore the fact that all the recovered files are now in a different physical disk, but they are not changed. :snapraid --find-by-name sync If everything was recovered, this command is immediate. Content SnapRAID stores the list and checksums of your files in the content file. It's a text file, listing all the files present in your disk array, with all the checksums to verify their integrity. You do not need to understand its format, but it's described here for documentation. This file is read and written by the "sync" command, and only read by "fix" and "check". blk_size SIZE Defines the size of the block in bytes. It must match the size defined in the configuration file. checksum CHECKSUM SEED Defines the checksum kind used. It can be "murmur3" or "spooky2". SEED is a 128 bits seed used in all the hash operations. From SnapRAID 2.0 the old "md5" checksum is not supported anymore. map NAME INDEX [UUID] Defines the position INDEX of the disk NAME in the parity computation. The disk UUID is also present if supported for the platform. sign SIGN Signature checksum of the content file to ensure that it doesn't get corrupted. If you want to modify the content file manually, you have to remove this line to avoid this check. file DISK SIZE TIME_SEC[.TIME_NSEC] INODE PATH Defines a file in the specified DISK. The INODE number is used to identify the file in the "sync" command, allowing to rename or move the file in disk without the need to recompute the parity for it. The SIZE and TIME information are used to identify if the file changed from the last "sync" command, and if there is the need to recompute the parity. The [.TIME_NSEC] information is optional, and only present if it's possible to read a such precise time information. It's present only from SnapRAID 2.0. The PATH information is used in the "check" and "fix" commands to identify the file. blk BLOCK HASH Defines an ordered parity block, part of the last defined file. BLOCK is the block position in the "parity" file. 0 for the first block, 1 for the second one and so on. HASH is the hash of the block. In the last block of the file, the HASH is the hash of only the used part of the block. new BLOCK Like "blk", but for new allocated blocks for which the hash is not yet computed, and the stored parity doesn't take into account this new block. This field is used only when you interrupt manually the "sync" command. chg BLOCK Like "blk", but for reallocated blocks for which the hash is not yet computed, and the parity is computed using the previous value of the block. This field is used only when you interrupt manually the "sync" command. hole DISK Defines the list of blocks that are deleted from a disk. This field is used only when you interrupt manually the "sync" command. off BLOCK Defines a block deleted from a disk, part of the last defined hole, for which the parity is computed using the previous value. This field is used only when you interrupt manually the "sync" command. inf BLOCK TIME Information shared by all the block at the specified offset. TIME is the last time of the hash/parity verification done at this block. symlink DISK PATH Defines a symbolic link in the specified DISK. hardlink DISK PATH Defines a hard link in the specified DISK. to PATH Defines where the previous symlink or hardlink links to. dir DISK PATH Defines an empty directory in the specified DISK. Directory that contains saved files, are not included, as they are implicitely defined in the file specifications. Parity SnapRAID stores the redundancy information of your array in the parity and q-parity files. They are binary files, containing the computed redundancy of all the blocks defined in the "content" file. You do not need to understand its format, but it's described here for documentation. These files are read and written by the "sync" and "fix" commands, and only read by "check". For all the blocks at a given position, the parity and the q-parity are computed as specified in: :http://kernel.org/pub/linux/kernel/people/hpa/raid6.pdf When a file block is shorter than the default block size, for example because it's the last block of a file, it's assumed as filled with 0 at the end. Encoding SnapRAID in Unix ignores any encoding. It simply reads and stores the file names with the same encoding used by the filesystem. In Windows all the names read from the filesystem are converted and processed in the UTF-8 format. To have the file names printed correctly you have to set the Windows console in the UTF-8 mode, with the command "chcp 65001", and use a TrueType font like "Lucida Console" as console font. Note that it has effect only on the printed file names, if you redirect the console output to a file, the resulting file is always in the UTF-8 format. Copyright This file is Copyright (C) 2011 Andrea Mazzoleni See Also rsync(1)